Electric switch



April l, 1947. 5 MlNNECl 2,418,363

ELECTRIC swITcH Filed Sept. 17, 1945 pgn.

lllllllllllllllllllllllllllllllIHHN /Z HIP Inventor: Sal vat ore Minnec,

by m

His Attorney.

Patented Apr. l, 1947 ELECTRIC SWITCH Salvatore Minneci, Pittsfield, Mass., assignor to General Electric Company, a corporation of New Yori:

Application September 17, 1945, Serial No. 616,908

(Cl. G-'16) 2 Claims.

rIhis invention relates to electric switches and lmore particularly to improvements in switches of the type in which a common contact makes selective engagement with a plurality of relatively .fixed contacts.

One use for switches of this nature is as a tap changer .For multitapped windings, such as the windings of a reactor or a transformer. Conventional switches of this type consist of a plurality of relatively xed contacts arranged in a crcle and connected respectively to the different taps, these contacts being engaged by a contact which rotates on an axis at the center of the circle. Ordinarily the full tap range voltage difference appears between two adjacent lixed contacts with the result that the size and spacing of the switch depends upon the magnitude of this voltage. This is undesirable as the voltage stress between adjacent pairs of xed contacts is nonuniform. In order to eliminate this diliiculty line type switches have been proposed in which the relatively fixed contacts are in a straight line and the movable contact moves in a straight line from fixed Contact to fixed contact. In this arrangement the end taps are connected to end contacts and intermediate taps are connected in the same sequence to intermediate contacts so that the spacing between xed contacts will inherently be proportional to the voltage difference between them.

In accordance with this invention I provide a novel and improved in-line type switch in which solid insulation is introduced between the movable Contact assembly and all of the fixed contacts, except the particular xed contact with which the movable contact is in engagement and in which the creepage distance along the solid insulation is automatically varied so that it is substantially proportional to the voltage difference between any xed contact and the movable Contact assembly.

An object of the invention is to provide a new and improved electric switch.

Another object of the invention is to provide a new and improved tap-changing switch.

A further object of the invention is to provide a new and improved high voltage ratio adjuster for electric induction apparatus.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 is a front elevation, partly in phantom, of a preferred embodiment of the invention; Fig. 2 is a sectional View taken on the line 2-2 of Fig. l; Fig. 3 is a sectional view taken on the line 3 3 of Fig. 1; Fig. 4 is a side elevation View of Fig. 1 taken on line 4-4, and Fig. 5 is a View similar to Fig. 4 but with the movable contact at the opposite end of its range of travel.

Referring now to the drawing and more particularlyto Fig. l, the switch may comprise end plates I and 2 which are held apart by'members 3 and 4. Merril er 3 is preferably of insulation, which may be a cylinder of Herkolite, as shown more clearly in Fig. 2, and member 4 is preferably made oi metal .so as to be an electrical conductor and which extends through the bottom plate 2 so as to form the common terminal of the switch. Extending transversely through the insulating cylinder t are a plurality of insulating members 5 which may also be of Herkolite and which `carry on their leithand ends metal contacts 6 which are connected respectively to cables I which may lead to different taps on a winding (not shown).

For making selective contact with the xed contacts 6 is a movable Contact assembly 8 which, as shown more clearly in Fig. 2, may comprise a pair of metal plates 9 which are fastened to a traveling nut Ill on a screw II which extends parallel to the members 3 and 4 and is preferably mounted for rotation in the end plates I and 2. It is shown as having an operating member in the form of a gear I2 on the outer top end thereof. The plates 9 have back extensions which embrace opposite sides of the metal rod 4 so as to make good electrical contact therewith.

For insulating the conducting parts of the movable contact assembly 8 from the fixed contacts 6 the parts are surrounded by a pair of concentric insulating cylinders I3 and I4 which may also be made of Herkolite. These are provided with oblique slots extending in opposite directions, these slots being just wide enough to allow the movable Contact plates 9 to pass therethrough.

The entire switch assembly may be submerged in insulating uid, such as mineral oil or askaral, which often lls or substantially lls the tank of a high voltage transformer. If so, it will be understood that the liquid will ll the cylinders I3 and I4.

The operation of the illustrated embodiment of the invention is as follows: With the movable contact assembly 8 in its top position, as shown in Figs. l. 2, 3, and 4, it will be seen that the distance between the slots at the bottom of the cylinders is a maximum and, as the voltage of the metallic parts of the movable contact assembly 8 corresponds to the voltage of the top xed contact 6, the voltage difference between the movable contact assembly 8 and the lowermost fixed contact 6 will be a maximum.

The dotted line in Fig. 3 shows the creepage path between the lowermost movable contact E and the metallic elements of the movable contact assembly 8 and it will be seen that this creepage path is relatively very long in comparison with the straight line distance between these metallic elements because of the fact that it extends in effect through a labyrinth in that it goes from the lowermost fixed contact 6 to the slot in the outer cylinder I3, then between the cylinders to the slot in the inner cylinder I4 and then to the parts 4 and Il. As will be seen from Fig. 4, the horizontal distance between the slots gets less and less as the vertical distance to the movable contact is decreased but as the voltage difference lbetween the movable contact and any fixed con- 1'. tact is proportional to the vertical distance be. tween them, the effective insulation and creepage distance is proportional to the voltage stress.

Fig. 5 shows how the creepage distance and the space between the slots and the cylinders automatically reverses when the movable contact is in its bottom position, which is as it should be because then the voltage between the movable contact assembly parts 4 and l I and the top fixed contact is a maximum.

With the movable contact in its mid-position the slots will of course cross each other so that ythe creepage distances between the end iixed 4 be understood by those skilled in the art that various changes and modifications can be made therein without departing from the invention and therefore it is aimed in the appended claims to cover all such changes and modications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States ls:

l. A switch comprising. in combination, a plurality of relatively xed contacts insulatingly supported in a straight line and adapted to be connected respectively to points in an electrical winding having progressively increasing voltage, a movable contact assembly for successively engaging said iixed contacts, said movable contact assembly including electrical conducting means extending generally parallel to the line of said re1- atively fixed contacts and spaced therefrom, a. pair of concentric insulating cylinders surrounding said last-mentioned means and having oppositely extending oblique slots, said cylinders being free to rotate, and a movable contact member extending through said slots and attached to said conducting means which extends generally parallel to said aligned iixed contacts.

2. In combination, a plurality of substantially aligned contacts adapted to have progressively different voltages whereby the voltage between any pair of contacts is generally proportional to the distance between them, a movable contact, means for moving said movable contact successively into engagement with said fixed contacts, solid insulation between said xed contacts and said means, and means for making the creepage distance of said solid insulation generally proportional to the voltage difference between said means and each fixed contact.

SALVATORE MINNECI. 

